I'll probably get told off for suggesting this but Whippet!
Medium sized check
Child friendly check
Calm temperament mostly a check 
they get calmer as they get older, my 3YO is lovely and chilled, 21MO is getting there, 9MO is still a bit of a giddy kipper. My lot are currently artfully draped on the sofa snoozing. I find it really, really relaxing being surrounded by sleepy sighthounds, they just seem to exude bliss.
Happy with a couple of moderate walks a day in the week and longer at weekend check, as long as they get the chance to run and stretch their legs properly my lads would be more than happy with 2 x 30 minutes a day. I walk them once a day and on average they get 45-60 minutes haring about off lead after which they're happy to laze on the sofa for the rest of the day. They're definitely sprinters, short bouts of hard exercise really satisfies them but they're also happy to do longer walks if the opportunity is presented.
Not yappy check, mine will sometimes alert bark if there is someone at the door but other than that they're not really barky at all. They do have a spectacular array of grumbles, whines and whinges though.
Not smelly check, they have very short and fine coats that are incredibly easy to keep clean, it takes them just minutes to dry after a bath generally only required when they've rolled in poo/something dead and they just generally don't seem to have much odour. My mum is not at all doggy and even she comments that our house doesn't smell particularly of dogs.
Utterly fabulous little dogs and I think they're often overlooked as family pets even though they really are perfect for the role.
Smaller independent rescues tend to be more likely to adopt out to families with young children rather than having blanket 'no children under x years' rules.